3D porous framework of ZnO nanoparticles assembled from double carbon shells consisting of hard and soft carbon networks for high performance lithium ion batteries.

Low electronic conductivity and large volume variation result in inferior lithium storage performance of ZnO. To overcome these shortcomings of ZnO, herein ZnO nanoparticles are encapsulated in resorcinol-formaldehyde resin-derived hard carbon and then further assembled into a 3-dimensional mesoporous framework structure using a polyvinyl pyrrolidone-derived soft carbon network. The synthesis methods include the polymerization of resorcinol-formaldehyde resin and a polyvinyl pyrrolidone-boiling method. ZnO@dual carbon has af large specific surface area (153.7 m2 g-1) and high porosity. It exhibits excellent cycling performance and high rate capability. After 350 cycles at 500 mA g-1, the ZnO@dual carbon still delivers a discharge capacity of 701 mAh g-1 while the actual discharge capacity of ZnO reaches 950.9 mAh g-1. At 2 A g-1, ZnO@dual carbon delivers the average discharge capacity of 469.6 mAh g-1. The electrochemical performance of ZnO@dual carbon is remarkably superior to those of ZnO@single carbon, pure carbon and pure ZnO nanoparticles, demonstrating the superiority of the dual carbon-assembly structure. This composite structure greatly improves the structural stability of ZnO, enhances its electron conductivity and overall electron transport capacity; which facilitates electrolyte penetration and Li ion diffusion, leading to improved cycling stability and good rate capability.